Concrete mixing drum



April 5, acKiNNEY TAL IApril 5, 1955 P. M.MaK|NNEY Erm. 2,705,521

CONCRETE MIXING DRUM Y Original Filed March 3, 1951 5 Sheets-Sheet w w 'mf mi w WW W W April 5, 1955 P. M. MaoKxNNl-:Y Erm. 3,705,621

CONCRETE MIXING DRUM Original Filed March 3, 1951 5 Sheets-Sheet 3 IM 'l April 5, 1955 P. M. .MaGKlNNEY Erm. 2,705,621

CONCRETE MIXING DRUM original Filed Maron s, 1951 5 sheets-sheet 4 ,MMU ,HMH um) 'IH IMI hl., mh IUI JWIN Mz-78576@ 071s April 5, 1955 P. M. MacKlNNl-:Y 4Erm.

CONCRETE MIXING DRUM original Filed March :5, 1951 5 Sheets-Sheet 5 MNM.

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zg/ @M @ZM United States Patent O CONCRETE MIXING DRUM Paul M. MacKinney and John Foster Oury, Melrose Park, Ill., assignors to Oury Engineering Company, Wheaton, Ill., a copartnership Substituted for abandoned application Serial No. 213,774, March 3, 1951. This application December 4, 1951, Serial No. 259,762

1s Claims. (c1. 259-161) This application is a substitute for our abandoned application Serial No. 213,774.

Our invention relates to a concrete mixing drum and preferably to a rotatably mounted mixing drum for use as a transit concrete mixer where concrete usually is partially or wholly mixed at a central mixing plant and transported away from the central plant to the point of use sometimes remote from the central plant, the drum preferably being an open ended type adapted to receive its charge of concrete mix through the open rear end and to discharge the contents through the saine opening at the point of use into forms for use in concrete building structures, foundations, and for floors, roadways, and the like, but the invention may be embodied in a standard closed drum and better and quicker mixing results obtained.

The primary object of our invention is to provide a rotatably mounted concrete drum angularly positioned upon a truck chassis in which a thorough mixing operation is accomplished or may be fully performed while in transit if desired, to the point of use, the drum being of a somewhat greater length than what has been normally used heretofore and in addition to the mixing operation the internal structure of the drum is adapted to force the material out of the drum by its reverse rotation, and preferably open at its rear end through which it is charged and through which its contents is discharged when mixed.

Another and further object of the invention is the provision of a concrete mixing drum whereby the concrete mix is moved longitudinally of the drum towards the forward part thereof against the hydrostatic head built up in the forward end of the drum whereby a more even distribution of the load carried by the drum is obtained upon the Wheels of the truck carrying the drum and the discharge of the load is also facilitated by being performed more quickly than what normally would be the case with the common type mixer and a more complete and thorough mixing is accomplished than what has been possible to accomplish heretofore.

Another and further object of our invention is the provision of a rotatably mounted elongated drum having continuously extending helical blades mounted on the inner surface of the drum in the form of a double Archimedes screw with a cover plate secured to the edges of adjacent blades whereby a helical tunnel is formed in the drum partially of its length and which as the drum is rotated thoroughly commingles the concrete mix by tumbling it laterally and also moving the mix longitudinally of the drum to an extent whereby the mix becomes piled up at the forward end of the drum, when continued rotation of the drum forces more of the mix against the lower portion of the mass of mix at the forward end of the drum causing the mix to flow rearward of the drum in an axial line along the center of the drum Where the mix will again be moved towards the forward end of the drum and the cycle of operation repeated as much as may be desired.

Another and further object of our invention is the provision of a mixing drum in which the material 1n the drum is positioned in the mixing drum in such manner that the capacity of the drum is materially increased in comparison with other drums of similar type so that something like an additional yard of concrete mix can be carried in a drum normally of the same overall dimensions as the drums commonly used, thereby decreasing the cost of transporting the concrete mix and enabling a larger amount of concrete mix to be transported in a given length of time.

Another and further object of our invention is the provision of a mixing drum in which a more thorough and complete mixing of the material is: performed while in transit, so that if desired, the material does not have to be mixed so thoroughly at the central plant and also, should it become necessary for a truck to stand at the point of use of the concrete for an unusual length of time, the drum can be operated, thereby separating the various parts of the aggregate which may have become adhered together in a mass so that it is discharged in a homogeneous fluid condition.

Another and further object of our invention is the provision of an elongated drum angularly mounted 0n a truck chassis in which the larger portion of the mix is carried in the forward end of the drum, thereby placing the major portion of the load between the front and back wheels of the truck on which the drum is mounted resulting in an increase in the load weight supported by each of the front wheels of the truck with a corresponding decrease in the load carried by the rear wheels, which distribution of load weight results in the mixer being able to carry a larger quantity of concrete without violation of highway regulations which limit the road weight each Wheel may carry and the like, and in which the forward end of the drum is positioned at a lower point on the chassis, thereby obtaining a low center of gravity for the load as a whole, while the discharge end of the drum is high enough to secure the proper distribution of the discrarged material by gravity through a chute if desire Another and further object of our invention is the provision of a mixing drum for use as a transit mixer avhich is capable of mixing a small amount of material as well as a quantity of material which substantially fills the drum to capacity.

These and other objects of my invention Will be more fully and better understood by reference to the accompanying drawings and in which- Figure 1 is a side elevation of our improved concrete mixer mounted upon a truck chassis;

Figure 2 is a longitudinal view of the mixing drum with the blades mounted therein in helical arrangement being shown in elevation.

Figure 3 is a longitudinal sectional view of the mixing drum and showing portions of the blades mounted therein;

Figure 4 is a view of the drum and blades similar to the View of Figure 3 taken at an angle of 180 to the view shown in Figure 3; and

Figure 5 is a View partially in section and partially in elevation showing a modified form of mixing drum.

Referring now specifically to the drawings and in which like reference characters refer to like parts throughout, a mixing drum 10 is shown of the usual form of concrete mixers except perhaps somewhat more elongated having an open rear end 11 with a ring 12 around the body of the drum at the rear end thereof with a track 13 extending circumferentially around the drum intermediate its ends and in engagement with rollers 14 mounted in blocks 15 which in turn are mounted upon a pillow block 16 mounted upon the chassis 17 of the truck. The forward end of the drum 10 is closed by a plate 18 having a bearing plate 19 secured thereto and within which an axle 20 is mounted which is secured in a bearing 21 mounted in a brack` et 22 secured to a front pillow block 23 also mounted upon the chassis 17. A sprocket wheel 24 is mounted upon the axle 20 and has a sprocket chain 25 passing thereover which leads to a suitable motor or power takeoff mechanism operated by the truck motor and which forms no part of this invention but provides means by which the drum can be rotated during the filling, discharge, and mixing operations, whether the truck is in motion or is standing, as the case may be.

At the rear end of the trucka charging chtite 26 is shown which extends into the drum 10 for delivering the concrete material into the mixing drum while a collecting chute 27 is provided which receives the concrete as it is discharged from the mixing drum 10 and delivers it into a hoisting bucket, directly to the ground or preferably into a distributing chute 28 which in normal inoperative position extends alongside of the drum 10 as shown in Figure l, and is mounted at its rear end upon a bracket 29 and swings horizontally thereon in its operative position and at the front end upon a bracket 30 secured to the chassis in any approved manner, but which forms no part of the present invention. A jack 31 is secured to the bracket 29 at one of its ends and to a bracket 32 attached to the spout 28 at its opposite end, and serves t0 support the spout 28 and also assists the operator in manipulating the chute to proper position. A frame 33 is provided, the lower ends of which are supported upon the truck chassis 17 and which extends upward adjacent the open end 11 of the drum 10 and has the charging chute 26 and the collecting chute 27 secured thereto independently of the drum 10, the frame 33 being supported by braces 34, 34 which are secured at one of their ends to the frame 33 and at their opposite ends to the pillow block 16.

Mounted internally of the drum 10 is a plurality of blades 35 and 36 which are secured at their outer edges to the wall of the drum 10, preferably by being welded thereto, these blades being formed from plates which are placed in end to end registered relation with each other and transverse substantially the length of the drum 10 in the same pitch in a spiral manner with their rear ends being secured to the drum at opposite sides of the drum or at an angle of 180 to each other, the blade 35 being longer by one-half the internal circumference of the drum 10 than the blade 36 so that they terminate in register with each other near the forward end of the drum 10, the blade 35 being positioned in the drum so as to make approximately 21/2 turns internally of the drum while the blade 36 makes approximately two turns in the drum. A cover plate 37 is provided which is welded or otherwise secured to the inner marginal edges of the blades 35 and 36 from a point near their rear end `to the forward ends of the blades 35 and 36 or to their point of termination adjacent to and towards the forward end of the drum 10. Two parallel passages 38 in the form of a tunnell and 39 open at one of its sides are formed in the drum by the blades 35 and 36 and the cover 37. The tunnel 38 extends intermediate the length of the drum 10, the purpose of the cover 37 being to prevent the material from piling up intermediate the ends of the drum over the internal edges of the blades 35 and 36 and to force the material towards the front end of the drum 10, after some Lmaterial has been charged into the drum, and has reached the forward end of the drum 10 in a somewhat small amount, and it becomes necessary to force such material upward at the forward end of the drum against the weight of such material and the hydrostatic head built up in the forward end of the drum. The drum 10 is being rotated by the power mechanism in a clockwise direction (as viewed by a person facing the rear end of the drum 10) and as the charging operation continues, the material builds up at the forward end of the drum to a point adjacent to or against the top of the drum, and thence ows rearwardly in somewhat of a tumbling movement axially of the drum 10 through the cylinder formed by the cover 37 and the material in the open passage 38 between the blades 35 and 36. While some of the material becomes commingled with material in the open passage 38, the major portion is ultimately caused to return toward the rear end of the cylinder 10 where it is again picked up by the blades 35 and 36 and again moved towards the forward end of the drum for another cycle of mixing. The cover 37 with the blades 35 and 36 force the material longitudinally, whereas if the tunnel 38 is not provided, the material is not moved longitudinally because of the resistance of the hydrostatic head. The rotation of the drum without the tunnel 38 merely causes a churning or tumbling of the material in a lateral direction and no longitudinal movement is obtained after a quantity of material reaches the front end of the drum.

In Figure 5 a modied form of drum is illustrated which is substantially like the forms already described herein with the exception that two plates 40 and 41 are secured to the blades 35 and 36 which are spiral in shape but shorter than the plate 37 and extend preferably only slightly less than three-fourths of a turn around the inner edges of the blades 35 and 36 and are spaced whereby an opening 42 is formed with two tunnels 43 and 44, respectively, being provided instead of one such as 38 in the preferred form, with the'open helical passage 39 being formed alongside the two tunnels 43 and 44.

We have found that where approximately the full capacity of the drum in its preferred form is used, the loading, the mixing operation in transit with both a wet and dry mix, with the water added to the dry mix while in transit, and the discharge operation are very satisfactory. When the full capacity of the drum is used of the preferred size, it will hold approximately four yards of material. When, however, it is desired to mix a smaller quantity, say one-half the capacity of the drum, it is not possible to build up a sufficient hydrostatic head in the forward end of the drum, because of the insufficient head created by the rotation of the drum in the stream of material towards the rear end of the drum, to cause the material to ow axially of the drum to the rear end. Therefore the mass of material is only churned or tumbled without suflcient longitudinal movement to obtain thorough mixing. The central core of material will ow a suicient distance rearward to enter the tunnel 44 through the opening 42 where it will again be moved toward the front end of the drum and throughly mixed. This modified form can also be used when the drum is filled to capacity, although there will be some loss of pressure built up by the tunnel and some mixing of the material at the opening 42, although the escape of material as it passes from the tunnel 43 to the tunnel 44 is prevented somewhat by the material flowing rearward over the opening 42 as the drum is rotated. Therefore, while there would be some loss of eiciency in the drum when operated with a full load of material, this loss is compensated for by the ability to mix a batch of material less in quantity than a full load.

[n the operation the device is exceedingly simple in that when the charging of the material into the drum takes place the truck on which the drum is mounted is positioned under -a discharge chute leading to a mixer where the aggregate is partially mixed, or to a suitable source of dry material, preferably mixed in the proper proportions, may be charged into the drum through the charging chute 26. As the drum is being lled the drum is rotated in a clockwise direction as seen by a person standing at the rear of the chassis and facing the drum, which operation is continued until a predetermined quantity of material is charged into the mixing drum. The quantity of material is determined by weight prior to its being charged into the drum and as the drum continues to rotate the material is moved longitudinally of the drum by the blades 35 and 36, a portion of the material being moved forward through the helical channel 39 while other portions of the material will enter the tunnel 38 and be moved along towards the front of the drum and ultimately discharged in the lower portion of the front of the drum where continued rotation of the drum builds up the material at the forward end of the drum, the material being fluid forms a hydrostatic head at the forward end of the drum which to a certain extent resists the head of the material being forced into the underside of the mass in the forward end of the drum until the mass is built up at the forward end of the drum until the drum is substantially filled at this point when it begins to flow backward axially of the drum over the surface of the plate 37 and over the material in the channel 39 and becomes somewhat commingled with the material in the channel 39 until it reaches the rear end of the drum where it is again picked up by the blades 35 and 36 and again forced toward the front end of the drum completing the cycle of operation. By the time the material returns to the rear end of the drum, the drum has received suicient material to constitute a normal substantially full load which load level is indicated by the full load line in Figure 5. When the drum receives its full quantity of lading the transit truck is driven away from the central loading plant towards the point of use and the drum continues its rotation during the trip for the necessary period of time to secure a thorough mixing of the material in the drum. Some mixing is accomplished by both a churning and a tumbling -action in a lateral direction as the material passes through the open channel 39 and in a longitudinal direction after the material enters the tunnel 38. If the cover 37 were omitted, the hydrostatic pressure at the forward end of the drum would overcome the pressure of the material against the hydrostatic head and the blades would merely cause a churning or a tumbling of the material without longitudinal movement and therefore a complete and thorough mixing operation would not be performed because the material would simply rise to a point where it would ow over the edges of the blades 35 and 36 and would not be moved towards the front end of the drum. Likewise, there probably would be a piling up of the material centrally of the drum. However, after the material enters the tunnel 38, it is confined within this tunnel by the cover 37, and cannot escape therefrom except at the forward end of the tunnel 38 as the material is forced along in the drum. Enough of the material is carried by the tunnel 38 to overcome the hydrostatic pressure developed at the front end of the drum, resulting in a backward flare of the material centrally of the drums. Therefore, all of the material ultimately passes ina cycle of operation to the front end of the drum, then upward, then backward through the median central tunnel formed by the cover 37 and over the surface of the material carried in the open channel 39 to the back end of the drum and this process repeated as often as may be desired. Should the complete mixing operation be performed in this drum, a quantity of water carried at some convenient part of the drum can be admitted to the drum during the rotation thereof, so that a complete mixing operation from dry mix to concrete of the proper wet constituency can be accomplished while the mixture is in transit.

When the load reaches its point of destination if the mixing has not been thoroughly accomplished, continued rotation of the drum can be continued or if there will be a material delay before the load is discharged, the drum is operated to keep the mix in a fluid condition until it is ready to be received and poured into its final position of a floor, forms, or the like as may be desired.

When it is desired to discharge the lading, the operator reverses the power mechanism, thereby reversing the rotation of the drum to a counterclockwise position as viewed by a person looking towards the rear of the drum which has the effect of forcing the material rearwardly towards the open end of the drum Where it is discharged into the gathering chute 27 as may be desired by the operator. As the material leaves the gathering chute 27 it is discharged directly to the ground or into the distributing chute 28 which is preferably mounted upon the frame 29 in such manner that it can be moved in an arcuate path to the rear of the drum and distributed onto a surface for use as a oor or into forms, or into a bucket to be elevated as may be desired depending upon the type of structure of which the concrete ultimately forms a part.

While we have described more or less precisely the details of construction, we do not Wish to be understood as limiting ourselves thereto, as We contemplate changes in form and the proportion of parts and the substitution of equivalents as circumstances may suggest or render expedient without departing from the spirit or scope of. the appended claims.

What is claimed is:

l. A concrete mixing drum comprising, in combination, a rotatably mounted drum open at one of its ends, a set of spiral blades mounted on the inner periphery of the walls of the said drum extending substantially throughout the length of the drum, and a cover plate secured to and spanning the space between the free edges of the said blades intermediate the ends of the said drum whereby at least one spiral tunnel is provided substantially throughout the length of the drum, said tunnel being uncovered adjacent the open end of the drum.

2. A concrete mixing drum comprising, in combination, a rotatably mounted drum open at its rear end, a plurality of spiral blades mounted on the inner periphery of the walls of the said drum extending substantially throughout the length of the drum and a cover plate secured to and spanning the space between the free edges of the said blades intermediate the ends of the said drum to form a spiral tunnel, the said tunnel being open at each of its ends, the rear end of the cover plate being spaced from the open rear end of the drum to provide an open receiving and discharge channel.

3. A concrete mixing drum comprising, in combination, a rotatably mounted drum open at its rear end, a pair of spirally blades mounted on the wall of the drum on the inner side thereof in spaced relation with each other extending from the open end and terminating adjacent the closed end and a cover plate secured to the edges of the said blades spanning the space between certain of the blades whereby a continuous spiral tunnel is formed in the said drum extending intermediate the length of the said drum, one end of the cover plate being spaced from the said open end of the drum to provide an open receiving space at the open end of the said drum.

4. A concrete transit mixing drum comprising, in combination, a rotatably mounted drum open at its rear end and closed at its forward end, a pair of spirally blades secured to the inside wall of the drum in spaced relation with each other and extending from the open rear end of the drum, the rear ends of the said blades being mounted on opposite sides of the internal wall of the drum at an angle of to each other and terminating at their forward end in register with each other, and a cover plate secured to and spanning the edges of the said blades to form a tunnel, the end of the cover terminating short of the rear ends of the said blades to provide a .receiving passage at the rear end of the said drum.

5. A concrete transit mixing drum comprising, in combination, a rotatably mounted drum open at its rear end and closed at its forward end, a pair of spiral blades secured to the inside Wall of the drum in spaced relation with each other, the rear ends of the said blades being mounted on opposite sides of the internal wall of the drum at an angle of 180 to each other and terminating at their forward ends in register with each other, and a cover plate secured to and spanning the edges of the said blades to form a tunnel, said tunnel being intermediate but spaced from the ends of the drum.

6. A concrete transit mixing drum comprising, in combination, a rotatably mounted drum open at its rear end and closed at its forward end, a pair of spiral blades secured to the inside wall of the drum and extending throughout the major portion of the length of the drum, the blades at one of their ends being mounted on opposite sides of the drum at 180" to each other and extending towards the opposite end of the drum whereby spiral passages are formed along the internal periphery of the said drum intermediate its length, and a cover secured to the edges of the said blades for a portion of their lengths whereby a covered spiral passage is formed towards the closed end of the drum but which is uncovered at the open end of the drum.

7. A concrete transit mixing drum comprising, in cornbination, a rotatably mounted drum open at its rear end and closed at its forward end, a pair of spiral blades secured to the inside wall of thedrum and extending throughout the major portion of the drum length, said blades at one of their ends being mounted on opposite sides of the drum and extending parallel with each other for the major portion of their lengths whereby two parallel special passages are formed in said drum, one of said passages being covered at its top for a substantial portion of its length and being uncovered at its top adjacent the rear end of the said drum.

8. A concrete transit mixing drum comprising, in combination, a rotatably mounted drum open at its rear end and closed at its forward end, a pair of spiral blades secured to the inside wall of the drum and extending throughout the major part of the drum length, said blades at the open end of the drum being mounted at opposite sides of the drum and extending toward the front of the drum to terminate in register with each other to define two spiral passages in said drum, one of said passages being closed at its top for a portion of its length near the forward end of the drum and both of said passages being open at the rear end of the said drum.

9. A concrete transit mixing drum comprising, in combination, a rotatably mounted drum open at its rear end and closed at opposite end, a pair of spiral blades secured to the inside wall of the drum and extending throughout the major portion of the drum length, said blades at the open end of the drum being mounted at opposite sides of the drum and terminating in register with each other near the forward end of the drum to define two spiral passages and a cover secured to the inner edges of the said blades in the forward portion of the drum, each of said passages being uncovered adjacent the open end of the drum.

10. A concrete transit mixing drum comprising, in combination, a rotatably mounted drum open at its rear end and closed at its forward end, a pair of spiral blades secured to the inside wall of the drum and extending throughout the major portion of the drum length, the

blades at one of their ends being mounted on opposite sides of the drum at 180 to each other and extending towards the opposite end of the drum whereby spiral passages are formed along the internal periphery of the said drum intermediate its length, and a cover secured to the edges of the said blades for a portion of-their-lengths, said cover having an opening therein intermediate its length.

11. A concrete transit mixing drum comprising, in combination, a rotatably mounted drum open at its rear end and closed at its front end, a pair of spiral blades secured to the inside wall of the drum and extending throughout the major portion of its length, the blades at one of their ends being mounted on opposite sides of the drum at 180 to each other and extending towards the opposite end of the drum to form spiral passages along the internal periphery of the said drum intermediate its length, and covers secured to the edges of the said blades enclosing one of said spiral passages throughout a substantial portion of its length, said covers being spaced from each other to form an opening for said one spiral passage intermediate its ends.

12. A concrete transit mixing drum comprising, in combination, a rotatably mounted drum open at its rear end and closed at its front end, a pair of spiral blades secured to the inner wall of the drum and extending throughout the major portion of the drum length, the blades at their rear ends being mounted on opposite sides of the drum at 180 to each other and extending towards the front end of the drum to form spiral passages along the internal periphery of the said drum intermediate its length, and a plurality of covers spaced from each other at their ends secured to the blades to partially close the top of one of the said passages.

13. A concrete transit mixing drum comprising, in combination, a rotatablyr mounted drum open at its rear end and closed at its front end, a pair of spiral blades secured to the inner wall of the drum and extending throughout the major portion of the drum length, the blades at their rear ends being mounted on opposite sides of the drum at 180 to each other and extending towards the front end of the drum to form spiral passages along the internal periphery of the said drum intermediate its length, and a plurality of covers spaced from each other at their ends and secured to the blades to cover the same passage and etect tunnels in spaced end to end relation with each other.

14. A concrete mixing drum comprising, a rotatably mounted drum open at its rear end and closed at its front end, a pair of spiral blades secured to the wall of the drum in spaced relation with each other, the rear end of each of the said blades being secured to the wall of the drum on opposite sides of the wall of the drum adjacent the rear end thereof and extending forwardly therefrom towards the front of the drum, and a cover secured to the edges of adjacent blades toward the forward end of the drum to form a tunnel in said drum, each of said blades leing uncovered adjacent the open rear end of the mixing rum.

15. A concrete mixing drum comprising, a rotatably mounted drum open at its rear end and closed at the front end, a pair of spiral blades secured to the wall of the drum in spaced relation with each other, the rear end of each of the said blades being secured to the wall of the drum on opposite sides of the inner Wall of the drum adjacent the rear end thereof and extending forwardly therefrom towards the front of the drum, and a cover secured to the edges of adjacent blades toward the forward end of the drum to form a tunnel in said drum, the rear end of the cover being spaced from the open end of the drum to form open channels at the rear end of the drum.

16. A concrete mixer comprising, a drum having its rear end open for charging and discharging, means detning a substantially tunnel-like spiral passage on the inner wall of the drum and extending over a major portion of j the drum length, the ends of the passage being open, said means being operative when the drum is rotated in one direction to move aggregates forwardly in the passage so that aggregates in the forward end of the drum move rearwardly centrally of said means and being operative when the drum rotation is reversed to move aggregates rearwardly in the passage, and conveyor means between the rear end of said passage means and the rear end of the drum for conveying aggregates to the open rear end of the passage when the drum is rotated in said one direction and to convey aggregates from the passage to the open rear end of said drum when the drum rotation is reversed.

17. A concrete mixer comprising, a drum having an open rear end for charging and discharging, a plurality of spiral blades on the inner wall of the drum and extending substantially from end to end of the drum, and means cooperating with adjacent ights of said blades to conne aggregates to the space between such blades and to dene a generally tunnel-like passage, said means extending over a major portion of the drum length and being spaced from the rear end of the drum so the blades adjacent the rear end of the drum act to deliver aggregates to or from said passage when the drum is rotated in its mixing or discharge direction respectively.

18. A concrete mixer comprising, a drum having its rear end open for charging and discharging, means de ning a substantially tunnel-like spiral passage on the inner wall of the drum and extending over a major portion of the drum length, the ends of the passage being open, the end of the passage nearer the open rear end of the drum being spaced from said rear end, and means carried by the drum between the rear end of the passage and the rear end of the drum for moving the drum contents toward or from the rear end of the passage.`

References Cited in the le of this patent UNITED STATES PATENTS 2,029,126 Rybeck Jan. 28, 1936 2,314,169 Smith Mar. 16, 1943 2,338,820 Peters Jan. 11, 1944 2,492,249 Willard et al. Dec. 27, 1949 2,678,197 Oury May 11, 1954 FOREIGN PATENTS 50,035 Switzerland Dec. 2, 1909 

